Hi Hollie
I work strange hours and sometimes need to get to sleep at difficult times when I'm not really sleepy. I bought a kind of hyponosis CD called Deep Sleep Every Night and although it didn't seem to work for the first week, in the end, bit by bit it worked so well that as soon as I hear the man's voice start speaking I'm off to sleep. I'm pretty sure you can get it on the internet so why don't you talk to your parents about it and see if they can help you buy it? Perhaps they can try it first so they're completely happy that it's safe for you to use.
Remember that worrying about something does no good to anyone and only makes you feel worse. You can't make this go away so there's no point allowing those thoughts to take you over. For the meantime, pick a really happy memory and whenever you feel the 'worry thoughts' come into your mind, force yourself to think about that happy time instead. Think about the colours, the sounds, the smells, the feelings, and let yourself become absorbed in that really happy memory. They're just thoughts, and you can control them with a bit of hard work on your part.
Good luck.